JPH06187949A - Electrodeless fluorescent lamp - Google Patents

Abstract

PURPOSE: To reduce electromagnetic hindrance and the dielectric loss of a ferrite core in an electrodeless fluorescent lamp such as having a solenoid driving coil wound around the ferrite core. CONSTITUTION: An inner shield 30 is provided between a coil 16 and a core 14, and an outer shield 40 is provided around the coil. Each shield has a sheet made of a soft dielectric material such as polyimide, and a vertical band made of metal is formed thereon. The metallic band is connected to earth in order to shield the core and a plasma from an electric field produced around a driving coil.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorescent lamp, and more particularly to a shield for an electrodeless fluorescent lamp which reduces electromagnetic interference (EMI) and dielectric loss of the core of a solenoidal drive coil.

[0002]

BACKGROUND OF THE INVENTION Electrodeless fluorescent lamps generally require less operating power than ordinary incandescent bulbs and are generally more efficient than incandescent bulbs on a lumens per watt basis.
Therefore, some electrodeless fluorescent lamps are designed to be used in place of incandescent bulbs in standard fixtures. Like typical incandescent bulbs, electrodeless fluorescent lamps have a bulb, or outer envelope. The bulb of the electrodeless fluorescent lamp is filled with a filling material of a conventional fluorescent lamp, that is, a mixture of a rare gas (for example, krypton and / or argon) and mercury vapor or cadmium vapor.
A solenoidal drive coil is provided in a recess recessed inside the bulb. In one electrodeless fluorescent lamp, the drive coil is wound around a ferrite rod, which acts as the transformer core, the coil acts as the primary winding of the transformer, and the gas filling is the transformer. Functions as a secondary winding.

When excited by a radio frequency (RF) power supply, an electric current flows through the drive coil, establishing a radio frequency magnetic field in the bulb which ionizes and excites the gas inside, resulting in a discharge. Generates ultraviolet rays. Ultraviolet light from this discharge is absorbed by the phosphor coating on the inside surface of the bulb, which stimulates the emission of visible light from the fluorescent lamp.

One problem with electrodeless fluorescent lamps is that EMI currents flow as a result of the electric field between the coil and the plasma. Such EMI currents typically exceed the limits set by regulatory agencies (eg, the Federal Communications Commission of the United States). Furthermore, in the case of an electrodeless fluorescent lamp using a ferrite core, the electric field between the core and the coil induces a current flow in the core, which results in another loss. This loss can result in heating of the core and extinction of the discharge.

Therefore, the EM produced by the electrodeless fluorescent lamp.
It is desirable to reduce I so that the electrodeless fluorescent lamp can be replaced with an incandescent light bulb over a wide range and to reduce the dielectric loss of the electrodeless fluorescent lamp when a ferrite core is used.

[0006]

SUMMARY OF THE INVENTION In an electrodeless fluorescent lamp having a solenoidal drive coil wound around an induction core, an inner shield is provided between the coil and the core and an outer shield is provided around the coil. The shield preferably comprises a sheet of flexible dielectric material on which a vertical band of etched metal is provided parallel to the axis of the core. The metal band is connected to ground to shield the core and plasma from the electric field generated around the drive coil. By shielding the core, the capacitance between the coil and the core is effectively shorted,
Virtually reduces or eliminates core dielectric loss. The outer shield effectively reduces the EMI generated by the drive coil.

The features and advantages of the present invention will become apparent upon a reading of the following detailed description of the invention in conjunction with the accompanying drawings.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a typical electrodeless fluorescent lamp 10 having a bulb or envelope 12 enclosing an ionizable gas fill. Suitable packings are, for example, noble gases (eg krypton and / or argon) and mixtures of mercury vapor and / or cadmium vapor. Recess 1 in which an induction transformer core 14 (for example made of ferrite) with a coil or winding 16 provided on the upper side is formed in the envelope 12.
It is provided in 7. The inner surface of the envelope 12 is coated in a known manner with a suitable fluorescent material that is stimulated to generate visible light when it absorbs ultraviolet light. Envelope 12 may optionally be mounted on the base of a fluorescent lamp, or may be fitted into a standard base assembly (eg, a standard Edison-type threaded plug not shown) for connection to a radio frequency power source external thereto.

In operation, current flows through winding 16,
A radio frequency magnetic field is established in the transformer core 14. The magnetic field in the transformer core 14 induces an electric field in the envelope 12,
This electric field ionizes and excites the gas contained therein, and as a result, a discharge 18 that emits ultraviolet rays is generated. Ultraviolet radiation from the discharge 18 is absorbed by the phosphor coating on the inside surface of the fluorescent lamp, thereby stimulating the emission of visible light.

In accordance with the present invention, the inner shield is core 14
And an outer shield provided between the winding 16 and the winding 16.
It is provided around. The inner shield functions to short-circuit the capacitance between the winding and the core, which substantially reduces or eliminates the core dielectric loss, and the outer shield substantially eliminates the EMI generated by the winding. Reduce. FIG. 2 is a plan view showing a preferred structure of the inner and outer shields according to the present invention. FIG. 3 is a perspective view of the shield of FIG. The shield is a sheet of dielectric material 22 (eg,
E. I. Dupont Denemore's and Company
ND de Nemours and Company) and has vertical metal bands 20 (eg, copper bands) formed by etching and deposited thereon. The metal band 20 is not continuous in azimuth to minimize eddy currents that effectively short the plasma. Further, the metal band is thin enough to prevent eddy currents that would otherwise cause losses in the coil from flowing in the cross section.

The metal bands 20 are connected to each other by horizontal conductors 24 formed on the bottom of the sheet 22 by etching. By providing a horizontal conductor at the bottom of the structure, the effect on the magnetic field established around winding 16 is minimized. Copper tabs 26 are provided that connect the conductors 24 to circuit ground to shield the core and plasma from the electric fields generated around the windings.
Sufficient space 28 is provided on each side of the stack so that the horizontal connection 24 does not form a shorted turn when the flexible shield is wrapped around the core. .

Advantageously, the use of such a stack of copper and Kapton polyimide film results in a very thin shield which does not require much space in the recess of the fluorescent lamp. Furthermore, the use of thin conductors reduces eddy current losses. And, although continuous metal bands can be used rather than the multiple bands shown, the use of multiple metal bands can minimize eddy currents. As a further advantage, the Kapton polyimide film has very high dielectric breakdown characteristics, so that the winding and the shield can be provided close to each other without risk of dielectric breakdown due to the electric field of the coil.

4 and 5 show an inner shield 30 constructed as in FIG. 2 wrapped around the core 14 such that the band 20 is parallel to the longitudinal axis 31 of the core. The Kapton polyimide film is shown mounted adjacent to the core with the copper band 20 exposed, but if necessary, the dielectric strength of the polyimide film is used to maintain the electric field between the winding and the shield. Alternatively, a copper band may be provided adjacent to the core to do so.

6 and 7, the winding 16 has an inner shield 3
0 shows how it is provided around 0, and FIGS. 8 and 9 show an outer shield 40 constructed as in FIG.
Is shown around the winding. (In FIGS. 8 and 9, dash (') numbers are used to distinguish components of the outer shield 40 from components of the inner shield 30.) According to another embodiment, The outer shield 40 is formed shorter than the drive coil 16 to expose at least the top winding of the coil, thereby discharging the electric field lines from the top winding of the coil to the grounded shield. May be pierced through to ensure the destruction of the gas for ignition of the fluorescent lamp.

In the case of electrodeless fluorescent lamps using a solenoid-like drive coil without a ferrite core, the outer shield according to the invention is provided around the winding in order to advantageously reduce the EMI generated by the winding. . While the preferred embodiment of the invention has been illustrated and described, it will be clear that such embodiment is merely an example.
Many modifications, variations and substitutions will occur to those skilled in the art without departing from the invention. Accordingly, the invention is limited by the spirit and scope of the appended claims.

[Brief description of drawings]

FIG. 1 is a partial sectional front view of a typical electrodeless fluorescent lamp.

FIG. 2 is a front view showing the shape of the shield of the electrodeless fluorescent lamp according to the present invention.

FIG. 3 is a perspective view of the shield of FIG.

FIG. 4 is a front view showing an inner shield wrapped around a core.

5 is a cross-sectional view of the inner shield of FIG.

FIG. 6 is a front view showing a structure in which a coil is wound around the inner shield of FIG.

7 is a cross-sectional view of the structure of FIG.

8 is a front view showing a structure in which an outer shield is wound around the coil of FIG.

9 is a cross-sectional view of the structure of FIG.

[Explanation of symbols]

 10 Electrodeless Fluorescent Lamp 12 Envelope 14 Core 16 Winding 17 Recess 20 Metal Band 22 Sheet of Dielectric Material 24 Conductor 26 Tab 30 Inner Shield 40 Outer Shield

Claims (11)

[Claims] 1. A phosphor material that contains an ionizable gas fill that sustains an arc discharge under a radio frequency magnetic field and, as a result, emits ultraviolet light, and that is excited by the ultraviolet light to emit visible light. A light transmissive envelope having an inner coating, and a winding disposed inside the envelope, the winding being connected to a radio frequency source to form the radio frequency magnetic field around the winding. And an EMI shield wrapped around the winding, the EMI shield having a plurality of metal bands disposed on a flexible dielectric material and connected to circuit ground. An electrodeless fluorescent lamp equipped with. 2. The electrodeless fluorescent lamp according to claim 1, wherein the winding is arranged around the induction core. 3. An inner shield disposed between the core and the winding, the inner shield having a plurality of metal bands disposed on a dielectric material, the metal shield comprising: The electrodeless fluorescent lamp of claim 2, wherein the band is connected to the ground of the circuit. 4. The electrodeless fluorescent lamp according to claim 1, wherein the metal band of at least one of the EMI shield and the inner shield is parallel to the axis of the core. 5. The electrodeless fluorescent lamp according to claim 4, wherein the metal bands are connected to each other by a conductor provided at a right angle to the metal bands. 6. The electrodeless fluorescent lamp according to claim 5, wherein the conductor is provided toward the bottom of the envelope. 7. The electrodeless fluorescent lamp according to claim 1, wherein the metal band of at least one of the EMI shield and the inner shield is made of copper. 8. The electrodeless fluorescent lamp according to claim 1, wherein the dielectric material of at least one of the EMI shield and the inner shield is composed of a polyimide film. 9. The electrodeless fluorescent lamp according to claim 1, wherein the EMI shield covers all winding parts of the winding. 10. The electrodeless fluorescent lamp of claim 1, wherein at least one winding portion of the winding is not covered by the EMI shield. 11. The electrodeless fluorescent lamp according to claim 10, wherein the one winding portion is the uppermost winding portion of the coil.